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The
easiest way to determine the sex
of adult Gila monsters is through ultrasound examination (for a complete
description of the technique including photos, click
here for the book Dr. Mark Seward's Gila Monster Propagation
). With this technique, an ultrsound is used to safely peer inside the
Gila to look for either testes or ovaries. This technique is best
performed during the winter or spring when a females ovarian follicles
are under development. In the past, many methods were
espoused.
Some people use body form to
differentiate the sexes. Males reportedly having broader heads and stouter builds. Females
reportedly having smaller heads, more elongated forms with bodies tending towards being
pear shaped. Please note that although some animals accurately reflect these morphological
differences, others are not easily sexed by form alone. At best it is an inconsistent
method.
Card and
Mehaffey (1994) published a method for differentiating the sexes radiographically.
They found a relationship between the length and width of the ischial arm (a bone in the
pelvic girdle) and the sex of the specimen. I have radiographed several of my Gilas and
have not been able to reproduce their results.
The surest way to sex Gilas was to
observe copulation or egg laying.
One thing is sure, during the
breeding season Gilas can tell the sex of one another. With a little experience,
observation of interactions between animals can often differentiate the sexes. Males will
not tolerate the presence of other males during the breeding season. They will react with
hissing and puffing as they wrestle for superior position in their ritualized combat
behavior. A male will respond to a female with a lot of tongue flicking and digging and
rooting around her. |
